In potentially explosive atmospheres such as on oil rigs or similar, mobile electronic devices such as mobile telephones or laptops are often used, which for the supply of electric energy can be connected via an appropriate external interface to a separate energy supply unit. In order to avoid an unwanted glow or spark ignition the battery or the electronic device can be equipped with a special electronic protective circuit. Such an electronic protective circuit may comprise circuits for limiting the electric current or energy, which prevent excessively high electric currents or energies from being present at the said electronic interface with the outside. Such an interface, in particular when using electronic devices in potentially explosive atmospheres, represents a special risk, because there is a danger that due to the electric energy present at the connection elements of the interface the possibly existing gas-air mixture may be ignited by a glow or spark ignition in the potentially explosive atmosphere.
The danger of a spark ignition primarily consists in that when the electric current present at the interface in the form of a current pulse or similar quickly rises over time. Such electric current pulses can occur in normal operation of the battery or the electronic device connected to the battery. A similar effect is achieved, when the electric poles of the battery—i.e. the minus and plus poles—provided at the interface are short-circuited, which in turn leads to a very quickly rising electric short-circuit current. An electric short-circuit can, as is known, be generated if an electric connection is inadvertently established between said battery poles; alternatively an error condition in the electronic device connected with the battery may be the cause of an electric short-circuit.
What can also happen is a glow ignition if the components of the battery or the electronic device including said interface between the battery and the electronic device become excessively hot. Such a warm-up may be the consequence of an inadmissibly high electric supply current between the battery and the electronic device, if this current exceeds the specified upper limit. Short-term current fluctuations or current pulses on the other hand, are unimportant with regard to an unwanted occurrence of a glow ignition.
In order to prevent the occurrence of a glow or spark ignition at the interface provided between the battery and the electronic device, the said electronic protective circuits must be designed in such a way that on the one hand, they react to a slow rise in the electric current beyond an admissible maximum value, but on the other hand, in the event of quick, pulse-like current fluctuations, guarantee a switch-off of the supply line. In addition the protective circuit must be able to detect, and prevent, an electric short-circuit in the battery or in the electronic device, which is supplied with electric energy from the battery.